300 



STUDIES IN THE EVOLUTION OF ANIMALS 



Great Sea-Dragons), had only three complete digits, and a 

 dwindling fourth in both hand and foot. 



All we can say is that mammals ^ may have started from a 

 branch of the great vertebrate series in which 

 the abnormality of five digits (we now call this 

 normal and archetypal) had already become a 

 fixed character, and not impossibly the abnormal 

 hands of the Plesiosaurs, with a reduction to 

 only five digits (Fig. 93), and also of their close 

 relatives, the existing Dolphins,^ may have been 

 the monstrous foundation of the whole race of 

 animals with five digits. We cannot for one 

 moment suppose that in the Ichthyosaur the 

 humerus, radius and ulna are the homologues of 

 the same bones in mammals, and at the same 

 time declare that the carpal, metacarpal, and 

 phalangeal bones of the same Ichthyosaur are 

 not homologous with bones of the same name in 

 mammals ! 



Well, some Ichthyosaurs have seven digits 

 and a dwindling eighth. What has become of 

 the sixth, seventh, and eighth digits in mammals? 

 The answer is, that not impossibly they 

 have been suppressed in past geological times, 

 as a deformity in the first instance, and after- 

 wards inherited as a normality ; that is, if mammals ever descended 

 from animals like the Ichthyosaur. Not only have three digits 

 been suppressed, but also a number of phalanges, and the whole 

 carpus, ulna, radius, and humerus have been vastly modified. 



^ Is there any good reason for supposing that Ichthyosaurs were 7iot mammals ? 

 - See figure of Round-headed Dolphin in Flower's Osteology of Mammals, p. 302. 





Fig. 93. — Left hand 

 of Plesiosaur, pi. 27, 

 Book of the Great Sea- 

 Dragons, by Thomas 

 Hawkins. 



